Reactors Couette flow reactor

Vaezi, V., E. S. Oh, and R. C. Aldredge. 1997. High-intensity turbulence measurements in a Taylor-Couette flow reactor. J. Experimental Thermal Fluid Science 15 424-31. 

Ouyang, Q. Swinney, H. L. Roux, J. C. Kepper, P. D. Boissonade, J. 1992. Recovery of Short-Lived Chemical Species in a Couette Flow Reactor, AIChE J. 38, 502-510. Ouyang, Q. Tam, W. Y. DeKepper, P. McCormick, W. D. Noszticzius, Z. Swinney, H. L. 1987. Bubble-Free Belousov-Zhabotinskii-Type Reactions, J. Phys. Chem. 91, 2181-2184. 

Concerning open spatial reactors, a first approach was provided by the so-called Couette flow reactor . In this quasi-one-dimensionalreactor, the transport is ensured by turbulent diffusion. Fresh reagents permanently renewed at each end allow the system to be maintained at a controlled distance from equilibrium. When operated in this reactor, the CIMA reaction lead to various spatio-temporal structures (oscillating fronts) as well as to a nontrivial stationary spatial structure (three stationary fronts) [58, 59]. However, this is... 

In domain II, the pattern is made of a triple front As seen in Figure 10a, a thin dark stripe develops parallel to the previous sharp front. The pattern is no longer trivial since the oxidation capacity of the chemical medium monotically decreases from one edge of the gel to the other. This pattern is similar to the stationary triple front structure previously observed in the Couette flow reactor [58, 59]. 

Modeling Front Pattern Formation and Intermittent Bursting Phenomena in the Couette Flow Reactor... 

The aim of the present study is to provide theoretical and numerical support for the recent experimental observations of sustained dissipative structures in the Couette flow reactor. Our goal is actually to demonstrate that the experimental chemical front patterns observed in this open reactor can be described by a reaction-diffusion process and to show that the observations are characteristic of a wide class of systems. More generally, we wish to identify the main ingredients required for a pattern formation and to develop a theoretical analysis of the bifurcations that produce those dissipative front structures. 

Two different reactions have presently been studied in the Couette flow reactor, namely the variants of the Belousov-Zhabotinsky [27-30, 32] and chlorite-iodide [29-33] reactions. The BZ reaction has revealed a rich variety of steady, periodic, quasi-periodic, frequency-locked, period-doubled and chaotic spatio-temporal patterns [27, 28], well described in terms of the diffusive coupling of oscillating reactor cells, the frequency of which changes continuously along the Couette reactor as the result of the imposed spatial gradient of constraints. This experimental observation has been successfully simulated with a schematic model of the BZ kinetics [68] and the recorded bifurcation sequences of patterns resemble those obtained when coupling two nonlinear oscillators. 

Symmetric feeding (uo = ui) will also be considered in Sections 4.1.2. and 4.1.4. For the sake of simplicity, the value of a in the system (3) is set independent of x, a > au, so that when switching off the diffusion process, all the intermediate cell points evolve asymptotically to the same stable reduced steady state on the upper branch of the slow manifold. A more realistic model should probably take into account a spatial dependence of a, so that a(x = 0) = uq and o (x = 1) = ui. In related models [27,. 68] of the Couette flow reactor experiments conducted with the BZ system by the Texas group, the role of a is played by a third variable which corresponds to a set of reactants whose concentrations can be considered as... 

The spatio-temporal patterns observed when performing numerical simulations of the reaction-diffusion model (3) are in many respects very similar to those observed experimentally in the Couette flow reactor with the CIMA reaction [31, 59-64]. This reaction provides a remarkable illustration that stationary and oscillating front patterns can organize in a chemical system from the diffusive coupling of steady state reactor cells. The aim of this section is to detail some specific transitions leading to spatio-temporal patterns... 

Fig. 6. The spatio-temporal variation of the variable u(x, t) is coded in order to mimic the spatial color profiles observed in the Couette flow reactor [31-33] 32 shades are used from the left-end upper branch (reduced) state (black) to the right-end lower branch (oxidized) state (white). The numerical spatio-temporal patterns in (a)-(f) are the same as in Figure 5.

In order to mimic sustained patterns observed in the Couette flow reactor with symmetric feeding [33], let us now consider symmetric Dirichlet boundary conditions uq and u are for example located on the (oxidized) lower branch of the slow manifold, while a still belongs to the (reduced) upper branch [61, 62,64]. Even though there is no asymmetry in the feeding, there still exists a concentration gradient in the system close to the two boundaries. 

If a fluid is placed between two concentric cylinders, and the inner cylinder rotated, a complex fluid dynamical motion known as Taylor-Couette flow is established. Mass transport is then by exchange between eddy vortices which can, under some conditions, be imagmed as a substantially enlranced diflfiisivity (typically with effective diflfiision coefficients several orders of magnitude above molecular difhision coefficients) that can be altered by varying the rotation rate, and with all species having the same diffusivity. Studies of the BZ and CIMA/CDIMA systems in such a Couette reactor [45] have revealed bifiircation tlirough a complex sequence of front patterns, see figure A3.14.16. 

The vortex flow reactor was a glass Couette cell driven by a Bruker RheoNMR system. The cell consisted of a stationary outer glass tube with an id of 9 mm and a rotating inner glass tube with an od of 5 mm, giving a gap of 2 mm. The Couette was filled with cylindrical bacterial cells, F. nucleatum ( 2 x 20 pm), suspended in water at a concentration of =10" cells mL-1. 

Preparation of Monodisperse, Spherical Oxide Particles by Hydrolysis of Metal Alkoxide Using a Couette-Taylor Vortex Flow Reactor... 

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